A twist drill of cemented carbide is manufactured from a cylindrical blank which is machined by grinding to a desired shape and dimension in particular to form cutting edges and flutes. As a result of the grinding, sharp edges are formed.
Solid cemented carbide drills are often most worn at the periphery of the cutting edge. This may be explained by the fact that the cutting speed is higher in the periphery, and consequently continuous wear mechanisms act more rapidly due to the higher temperature generated in this zone. However, discontinuous wear mechanism is often the cause of the wear in the periphery, e.g. adhesion wear acting at the main cutting edge can in the end cause breakage of the edge. In order to suppress the adhesion wear, the cutting edges are made as sharp as possible to reduce the cutting forces.
An object of the invention is to provide a twist drill with increased tool life.
It is a further object of the invention to provide a twist drill with reduced wear in the corner between the main cutting edge and the leading edge.
It is yet a further object to provide a method of making a twist drill with increased tool life.